The polyphenylene sulfide resin (hereinafter abbreviated as PPS resin) has a high melting point and has favorable properties as engineering plastic, for example, excellent flame resistance, rigidity and chemical resistance. The PPS resin is molded mainly by injection molding and is used in a wide range of applications including various electric and electronic components, mechanical components, automobile components and home electric appliances. The PPS resin material having the excellent heat resistance and the good flowability has been highly demanded to meet the latest needs for modularization of large components for automobiles and reduction of the wall thickness of molded products accompanied with weight reduction. The PPS resin alone, however, has the problem of insufficient rigidity at high temperatures by reduction of the wall thickness of the molded product. The PPS resin mixed with an inorganic filler such as glass fibers has, on the other hand, a significant increase in melt viscosity, while improving the heat resistance and the rigidity. This causes problems such as an increase in outgas amount by high shear heat generation during injection molding and deterioration of the molding processability.
In the development of the PPS resin to the application of automobile lighting components that need the excellent surface smoothness and rigidity, since the PPS resin alone has insufficient rigidity, the known technique mixes an inorganic filler with the PPS resin. This, however, fails to provide a molded product of the sufficient performance. Especially when a molded product is produced by mixing an inorganic filler with the PPS resin, the insufficient adhesiveness with the filler causes the uneven distribution of the filler on the surface of the molded product and the increased irregularities on the surface of the molded product. This fails to provide the sufficient surface smoothness and needs secondary processing such as undercoating for formation of the mirror surface by coating the molded product with a metal such as aluminum, thus undesirably reducing the mass productivity. Recently there has accordingly been high demand for the PPS resin material having the excellent surface smoothness and rigidity.
By taking advantage of its characteristics, the PPS resin has also been recently employed for plumbing components such as piping components in which oil passes through and home water heater piping components in which water passes through. The PPS resin alone, however, has not enough toughness that is important especially in plumbing components and is likely to cause a crack of piping by freezing. A technique of mixing an olefin resin with the PPS resin has been studied previously to prevent the freezing-induced cracking. The conventional technique of mixing an olefin resin improves the toughness but has the disadvantage that significant reduction of the rigidity at high temperature is likely to cause thermal deformation. A generally employed technique further mixes an inorganic filler, in order to solve the problem of the reduced rigidity at high temperatures by mixing the olefin resin. Mixing the inorganic filler improves the rigidity, but significantly deteriorates the toughness and additionally has the disadvantage of deterioration of the molding processability by an increase in melt viscosity. In order to solve such problems, there is a high demand for the PPS resin material satisfying both the toughness and the rigidity at the high level and having excellent molding processability.
For example, Patent Document 1 discloses a resin composition by mixing polyphenylene sulfide with a weight loss percentage ΔWr of not greater than 0.18% under heating with fibrous and non-fibrous fillers. The resin composition described in Patent Document 1 has the reduced outgas amount and improvement in material rigidity but has the problem of the significantly reduced flowability. The resin composition described in Patent Document 1 additionally fails to sufficiently improve the adhesiveness with the filler and thereby fails to achieve the sufficient level of surface smoothness and rigidity.
Patent Document 2 discloses a PPS resin composition by mixing polyphenylene oxide as an amorphous resin and glass fibers having the fiber diameter of not greater than 7 μm. The PPS resin composition described in Patent Document 2 improves the molding shrinkage in the thickness direction by mixing the amorphous resin and has an effect of improvement on the surface smoothness to some extent. This, however, does not improve the adhesiveness with the filler and still causes the uneven distribution of the filler on the surface of the molded product, thus failing to provide the sufficient level of surface smoothness.
Patent Document 3 discloses a PPS resin composition by mixing a fibrous filler and a particulate filler in a specific shape. The resin composition described in Patent Document 3 tries to satisfy both the surface smoothness and the rigidity by combined use of the filler having the small particle diameter and the fibrous filler. This, however, fails to sufficiently improves the adhesiveness of the PPS resin with the filler and accordingly fails to provide the sufficient level of the surface smoothness of the PPS resin composition for the practical use.
Patent Document 4 discloses a PPS resin composition by mixing an ethylene.α-olefin copolymer having a glass transition temperature of not higher than −50° C. and an inorganic filler. The resin composition described in Patent Document 4 improves the rigidity by mixing the inorganic filler but has the problem of reduction in toughness at low temperatures. This resin composition is accordingly not the satisfactory level for the actual use.
The polyphenylene sulfide having the weight loss percentage ΔWr of not greater than 0.18% is known by Patent Document 5. Patent Document 6 describes a resin composition by mixing an epoxy group-containing olefin copolymer and an olefin copolymer without containing epoxy group with such polyphenylene sulfide. The resin composition described in Patent Document 6 reduces the outgas amount and improves the molding processability but does not have sufficient compatibility of the PPS resin with the epoxy group-containing olefin resin, thus failing to provide the sufficient toughness.
Any of these patent documents fails to teach a composition by mixing different PPS resins having different weight loss percentages ΔWr under heating and, as the result, a composition that solves the above problems of the PPS resin composition.